Temperature-control system



May 29, 1928.

A. J. KERCHER ET AL TEMPERATURE CONTROL; SYSTEM Filed March 5, 1927 :L: IIE .L FIE E S www c N cu/.R SMV O mi n T A mdwlwf Ve n WMMT# fu AM. Y B

Patented May 29, 1928. v

UNITED STATES PATENT OFFICE.

.ARTHUR J'z KERCHER, 0F BERKELEY, AND WILLIAM WESLEY HICKS, 0l' SAN FRANCISCO, CALIFORNIA.

TEMPERATURE-CONTROL SYS'IEM.

Application filed March 5, 1927. Serial No. 173,110.

This invention relates generally to systems for controlling the temperature of a medium being heated, and has special application to electrical heating systems in which it is desired to maint-ain the temperature of a medium between certain limits.

It is an object of this invention to devise a novel method and system of control for electrical heating systems, which will minimize sudden fluctuations and will tend to keep the temperature of the medium being heated substantially constant.

' It is an object ot this invention to devise a temperature control system and a method of operating the same which will be provided with means in addition to the usual temperature responsive element Jfor minimizing temperature iiuctuations.

It is a further object of this invention to devise control means for an electrical heating system which will operate to recurrently open and close the circuit to the heating element after the temperature of the medium has reached a certain maximum limit and before the temperature has dropped below a certain minimum limit.

It is a further object ot this invention to devise a novel form of switching means for controlling the current supplied to electrical heating elements. the switching means serving to repeatedly open and close the heating circuit after the closing of a. thermostatically controlled circuit.

It is the urtherobject of this invention to devisel a novel form of electrical switch which will be automatically actuated in response to the closing of the control circuit, the switch incorporating an expansible cell having a buckled diaphragm.

It is a further object of this invention to devise an lelectrical control system for a heatingdevice which may be adjusted so as to become inoperative after a predetermined lapse of time.

Further objects of the invention will appear from the 'following description 1n which we have set forth the preferred embodiment of our invention. It is to be understood that the appended claims are to be accorded a range of equivalents consistent with the status of the prior art.

Referring to the drawing:

Figure 1 is a side elevational view of an automatic switch suitable for incorporation with the system of this invention.

' Fig. 2 is an end view of the switch shown in Fig. 1. v

Fig. 3 is a plan view of the switch shown in Fig. 1.

Fig. Ll is a ci cuit diagram illustrating the system of this invention with the cell shown expanded and the switches shown in open circuit relation.

The invention comprises generally an electrical heating element which is in thermal contact with the medium being heated and which is energized from a main circuit. For opening and closing the main circuit there is provided an automatic switch which is actuated in response to the opening and closing of a control circuit. The control circuit includes a temperature responsive eleme-n` which. is also in thermal Contact with the medium being heated. The control circuit and automatic switch are interrelated in such a manner that when the control circuit is closed in response to a predetermined maximum temperature condition of the medium, the switch repeatedly opens and closes the main circuit at timed intervals until the control circuit vis opened, after which the switch remains closed. The repeated opening and closing of the main circuit after the medium has been heated to a certain maximum temperature tends to supply suicient heat to the medium to normally keep it at practically constant temperature. A device is also provided in conjunction with the automatic switch for timing operation of thev system.

Referring first to the system as shown in Fig. 4, the mediumv to be heated has been diagrammatically indicated at 10 and may consist of a gas, liquid or a solid. In thermal contact with this medium there is alleating element 11, this clement being energized from a main circuit which includes the current supply lines L, and L2. For controllin the main circuit there is provided the usua line switch 15 and an automatic switch indicated generally at 12, which for example may he. of the type which employs an expansiblc cell as disclosed and claimed in the copcnding application of A. J. Kercher No. 665.704 filed September 29, 1923. A switch ot this type. is desirable since it is relatively slow in operation, in other words it requires a considerable time after heilig energized by an electrical current for the switch to open, and a corresponding amount of time for the the construction of A engage'and' retain the switch ing that the mediurn'lO isinitially switch to automatically close after the exciting current has been interrupted. The switch as it has been diagrammatically shown in this view includes relatively movable contacts 13 and 14 which are con nected in series with line L1. .Contact 14 is mounted upon the lever 16 which is pivotally mounted as at 17 and is provided with a projecting linger'18 contacting -with the diaphragm of an expansible metallic cell 19, which will be` presently described. In thermal contact with the expansiblecell 19 there is an electrical heating element 21 which is energized from a control circuit indicated generally at 22. This control circuit includes the relatively movable contacts 23 and 24 of a thermostat element, and by means of conductors 27 and 28 is connected across the heating element 11. Any suitable kind of'temperature responsive element may be employed although for the sake ofreliability we prefer to use a metal rod 26 having a relatively high coefficient of expansion, one end of this rod being fixed while the other end carries the movable contact 23. p

In order to time operation of the system there'is provided a suitable clockwork mechanism 31. This timing mechanism serves to drive a cam 32 ata definite rate of speed. The rotation of cam 32 is indicated as being controlled by means of a visual setting device 33. Cooperating with cam 32 there is a latch 34 pivotally mounted as at 36 and biased as by means of spring 37 so as to normally be in position to engage thelever 16 when this lever is actuated to open contacts 13 and 14. A portion 38of this latch engages the cam 32 So as to retain the latch out ofengagement with lever 16 during normal operation of theswitch. However when cam 32 is rotated to a position to permit portion 38to ride upon the depressed cam surface '39, latch 34 will move to aposition toy l lever 16'in` open position. n J

4In explaining' the operation o f the system asfdescribedabove it will bepresumed' that thef'rnain'l circuit is energized Iby closing of line switch 15and 'switclilever 1-6.y Assumrelatively cool'and that contacts`13 and'14 are closed, the Aheating element' 11`will beenergized to increase the temperature 'of medium 10. When thetemperature reaches a certain predetermined maximum value contacts 23` and 24 are'clo-:ed by expansion of rod 26, thus placing'resistance 21 directly in shunt with heating element-11. Resistance element 21 will therefore be energized to supply heat t0 the expansible cell 19, and expansion of this cell serves to move switch lever 16 to open contacts 13 and 14 thus interrupting supply of current to the heating element 11. Re sistance 21 is also de-energized with opening tacts 13 and 14.

so that cam 32 v parts Aof the switch therel is remesa of contacts 13 and 14 sothat expansible cell 19 cools and again permits contacts 13 and 14 to close to reestablish the circuit., After the main circuit has again been established resistance 21 is again energized .to supply heat to expansion cell 19 and to open con- `'This opening and closing of the switch occurs repeatedly at regular timed intervals as long as contacts 23 and 24 remain closed, and in practice is sufficient to normally maintain the temperature of medium 10 substantially constant. However if the temperature of medium 10 drops below a certain minimum value due to dissipation of heat to other bodies or to the switching in of a heating resistance having a lower power consumption, then contacts 23 and 24 are opened, and upon the closing of contacts 13 and 14 resistance 21 will not be energized so that the switch will remain closed until the temperature has again lbeen raised to the maximum value. The resultant effect of the system is therefore to heat the medium up to a certain maximum temperature, then to supply heat intermittently and. at intervals sufficiently close together to keep the temperature substantially constant, and in case the temperature in time falls below a given minimum value to supply heat continuously until it has again reached the maximum value. Clockwork mechanism 31 may be utilized as a time control of the system and may be set can effect the engagement or disengaeement of latchy 34 with lever 16.

One ferm of automatic switch suitable for use with the system described above is shown vided 'with portions 51 which engagethe-- face of the buckled diaphragm 48. To'provide a lnounting for the various operablel provided a back plate 52. The expansible cell 46 is secured to a suitable support member -53 as-by means of screws 54. this support member 53 being preferably of insulating material *which is a poor conductor of heat. `Bolts 56 serve to retain support 53 and back plate 52 together, spacers 57 being employed apart a certain distance.

Y The Vinsulating support 53 1s retalned in operative position to keep the saine by means of brackets 58 which are also cngaged by bolts 56. Spacers 59 serve to posu1t1on the switch levers 44 in proper rela-4v tionship with respect to the expansible cell 46 so that when the diaphragm 48 is buckled inwardly the switch contacts are closed. In-

serted between the insulating support 53 and nection. terminals 63` which may be conveniently mounted upon the insulated support 42. Connection terminals 64 may also be provided for the stationary switch contact 41 in order to make possible convenient connection with the temperature control. system. When ,the switch contacts are intended to be connected in series with' only one side of the current supply lines, the movable contacts 43 are connected together by means of the flexible insulated conductor 66.

In order to permit control of the automatic switch from a timing or clockwork mechanism, there is provided a latch 67 which is mounted upon the insulated support 42 as by means 'of a resilient L-shaped strip 68. Each of the switch levers 44 is provided with a projecting portion 69 which is 'adapted to engage the latch and retain .the switch levers in op'en position for one position of latch 67. This'latch is intended to be controlled by a cam or other actuator operated from suitable timing mechanism such as explained with reference to the system of Fig. 4.

In operating a switcher' this kind when the heatingelement 61 is energized to supply heat to the cell 46,- expansion of gassen-v closed within the cell reaches a predetermined pressure after which the diaphragm 48 will be suddenly moved outwardly to-its outer buckled position. This movement oi the diaphragm lifts switches levers 44 to open thes'witch contacts, and as the movement of the diaphragm is very rapidpractically no arcing willoccur. 'When the eur- .rent sup lied to heating element 61 is interrupt the expansion cell 46' cools and when its internal'pressura has fallen below a predeterminedA value the diaphragm 48 is again forced inwardly by'pressure of the outer atmosphere to permit the switch contacts to close. 'The particular advantage in using a buckled diaphragm is that it dispenses lwith complicated mechanism for Securing quick opening of the contacts.

The system of this invention is particularly adapted for maintaining enclosed masses of iluid at practically constant temperature. For example it may be used for controlling the temperature of an electrical oven or for controlling the temperature of tanks of Water. vBecause of its inherent mode of operation separat-ion between contacts.23 and 24 of the temperature responsive element generally takes place when the v automatic switchcontacts 13 an. 14 are open,

with the result that no arcing occurs. For

this reasonth'e4 operation of the temperature responsive element is made more reliable and it may be constructed so that only a slight amount of movement is given to the contacts 23 and 24. Accordingly it is practical to employ simply a solid metal rod of the type indicated, thus obviating troubles due to molecular slippage as is experienced with loi-metallicthermostats.

l'Ve claim:

1. In a system for controlling the temperature of a medium, electrical neans for heating said medium, an electrical circuit for energizingv said heating means, and means for effecting timed variations of current supplied to said heating means after the temperature of the medium attains a certain maximum value. A

2. In a system for controlling the temperature ot' a medium, electrical means for heating said medium, an electrical circuit for energizing said heating means, and means for interrupting said circuit at timed intervals after tlic temperature of the medium attains a predetermined maximum value.

3. In a system for controlling'the temperature ot a medium, electrical means for heating said medium, an electrical circuit for energizing said heating means, a temperature responsive element thermally asseciated with said medium, and means conmediuin, and. means controlled by said element to open said circuit and repeatedly close the same when the temperature of the medium reaches a predetermined maximum value, and to maintain the circuit closed` when the temperature of the medium falls below a predetermined minimum value.

5. In a. system for controlling the temmil perature of a medium, electrical means for heating said medium, an electrical `circuit for energizing said heating means, a tem- `mi perature responsive element thermally as-l closing said circuit, and means for rendering said last named means inoperable ,to close the circuit after the lapseof ai predetermined period of time.

7. In a system for controlling the temperature of a medium, electrical means for heating said medium, a main electrical circuit for energizing said heating means, a temperature responsive element thermally associated .with said medium, a control circuit adapted to be closed by said element when the temperature of the medium reaches 'a predetermined value. and means controlled by said control circuit for repeatedly opening and closing said main circuit While thc control circuit reniainsclosed.

8. In a system forc'ontrollingthe temperature of a medium, aheating elementfor heating said medium; a main circuit for energizing said element, a temperature responminimum value, and then supplying heat* continuously luntil the temperaturev again reaches said maximum value.

In testimony whereof, we have hereunto set our hands.

ARTHUR J. KERCHER. VILLIAM WESLEY HICKS. 

